The invention is generally related to the field of post-etch residue removal in semiconductor fabrication and more specifically to a dry process for post-etch residue removal.
In semiconductor fabrication, layers are routinely patterned with photoresist and subsequently etched to create patterned structures. One example is a via etch in which a via or hole is etched through an interlevel dielectric to an underlying metal interconnect layer. A photoresist stripping process is then used to remove the photoresist pattern. The etch and strip processes leave residue on the surface of the structure. A cleanup process is then required to remove the residue.
In optimizing a process for residue cleanup, four types of residues are distinguishable, and appear to require some changes in process parameters in order to most efficiently remove the residues. The first type of residue is referred to as xe2x80x9cedgexe2x80x9d residue. Edge residue is found around the perimeter of the wafer and is comprised of photoresist scum that is not exposed to the in situ ash process due to a wafer clamping mechanism. A second type of residue is referred to as xe2x80x9csurfacexe2x80x9d residue. Surface residue is observable around vias and other patterned structures. The residue is unreactive with typical photoresist strip processes, and therefore remains after the strip process, whether or not the strip is in situ or ex situ with the dielectric etch process. The residue can be difficult to remove once it has been exposed to the ambient. A third type of residue is referred to as xe2x80x9cfeaturexe2x80x9d residue. Feature residue forms during the dielectric reactive ion etch (RIE) process and may cling to the sides of the feature or may accumulate at the bottom of the feature. For vias, when this type of residue is abundant, it can lead to a xe2x80x9cstop etchxe2x80x9d condition, in which the process conditions produce a polymer plug inside of the via rather than etching through the oxide interlevel dielectric layer. The fourth type of residue is referred to as a xe2x80x9cfieldxe2x80x9d residue. The field residue may be similar to the surface residue in quantity and composition. The field residue may differ from surface residue, because surface residue may incorporate more etch products due to its closer proximity to pattered areas compared with field locations. The residue may, therefore, be more difficult to remove for surface compared with field locations.
As device features of integrated circuits become smaller, currently used wet cleans become less effective in removing via or other feature residue. The fluid dynamics and surface tension properties of the liquids currently used limit their applicability to lower aspect ratio conditions compared with dry cleanup processes. Accordingly, an improved residue cleanup process is desired as aspect ratio requirements of the etch and cleanup move to more challenging feature sizes (larger aspect ratios).
The invention is a cleanup process that uses a dilute fluorine in oxygen chemistry in a downstream plasma tool to remove organic and inorganic polymeric residues. The cleanup process may remove undesired material and/or modify the exposed surface, thereby enhancing the desired properties of that surface.
An advantage of the invention is providing a cleanup process that offers simultaneous removal of both organic and inorganic residues using a dry (solvent-free) process.